1. Field of the Invention
This invention relates to the mechanical closing of rectilinear Pittsburgh lock side seams of metal duct sections, and most advantageously to the side seams of that type of duct section having integral end flanges.
2. Description of Related Art
"Pittsburgh" type lock joints are commonly used to join the seams of metal ducts, whether the sections are rectilinear, tapered or rounded. In all these types, seam closing has traditionally been accomplished by manually hammering the margin of the seam against the duct wall (peening). Disadvantages of such peening include the time required and the almost intolerable noise produced.
For closing rectilinear longitudinal joints, a three-roll seam closer machine has recently been made available by Iowa Precision Industries, of Cedar Rapids, Iowa. This machine mounts, on a carriage, a succession of three rolls, the first of which bends the outstanding margin to be closed through an approximate 30.degree. angle, the second bends it to 60.degree. and the third closes it to 90.degree.. A disadvantage of this type of machine, especially significant where the duct sections have integral outstanding end flanges, is that a substantial length--at least several inches at each end of the seam--must first be peened, to allow for the width taken up by the three carriage-mounted rollers which cannot pass these end flanges.